HAS OUR CLIMATE CHANGED?
POPULAR OPINION ERRONEOUS, AS THERE IS NO CHANGE WITHIN THE
PERIOD OF AN INDIVIDUAL LIFE, BUT MOMENTOUS CHANGES HAVE OCCURRED
SINCE THE BEGINNING OF THE CHRISTIAN ERA
One of the hallucinations entertained by nearly every adult person
is that the climate has changed since he was young. No matter what
the scientists may say, he knows that it has changed. Fifty years
ago did he not trudge to school for months every winter in snow
knee-deep? Have not the old swimming holes in the brook dried up?
Yes, he is a positive witness to an affirmative answer. Even the
river of his boyhood, whose broad expanse he conquered in a swimming
contest at the tender age of ten—as he views it after an absence of
a quarter-century—has dwindled to little more than a creek, across
which one easily may hurl a stone. Talk to him about no change in
climate. He’s been right on the spot, and knows. For all this, there
has been no change during the lifetime of this man; nor has there
ever been during the life period of any individual. Mutations, to be
sure, are going on all the time, but they are so minute that they do
not accumulate a measurable quantity except in periods of hundreds or
thousands of years. It is not the climate that has changed; it is the
man. The natural action of the stream may have filled the swimming
holes; or the stream may have entirely disappeared through much of
the contiguous area being brought under cultivation and the water
that formerly supplied its flow being utilized in the production of
cultivated crops, which actually make use of as much if not more
rainfall than the forest that formerly lined its sinuous banks and
covered the near-by lowland. And then, snow knee-deep to a boy of ten
hardly comes up to the ankles of a man of six feet two. Again, no one
can remember the climate of his boyhood; he cannot carry the average
in his mind; all that he can remember are a few instances of unusual
conditions which because of their unusual character left an impress
upon his mind. The river is just as wide as it ever was during the
period of his lifetime, or that of his father, or of his grandfather;
but he has lived on the broad Mississippi for many years, and when
he goes back to the scenes of his youth, his concept of what
constitutes a river has undergone a revolutionary change since he
left the parental roof to go forth and conquer the world.
An examination of the personal papers of Thomas Jefferson, in the
State Department at Washington, by an official of the Weather Bureau,
revealed a number of most interesting incidents in connection with
the weather observations made by the author of the Declaration of
American Independence. He says:
“A change in climate is taking place very sensibly. Both heats
and colds are becoming much more moderate within the memory of
even the middle-aged. Snows are less frequent and less deep. They
do not often lie below the mountains more than one, two, or three
days, and very rarely a week. The snows are remembered to have
been more frequent, deep, and of long continuance. The elderly
inform me that the earth used to be covered with snow about three
months in every year.”
But Jefferson and his neighbors were mistaken. Never during the
period of authentic history has the snow covered the ground in
Virginia an average of three months per year, or three months for a
single year. These old inhabitants were like those of to-day, who
remember only the abnormalities of climate of twenty-five or fifty
years ago, and in comparing the unusual conditions of long ago with
the average of the present time they are deceived. I have known
intelligent and well-meaning persons to declare that they knew from
personal recollection that the climate of their particular places of
residence had changed since they were young; that they had stable
landmarks to show that the streams were drying up, the rainfall
growing less, and the winters becoming milder, notwithstanding the
fact that carefully taken observations of temperature and rainfall
for each day for over one hundred years right at their places of
abode showed no change in climate. We have a continuous daily record
for one hundred years at New Bedford, Massachusetts, nearly as long
records at several other places, and numerous records for over half a
century. From these we learn that there has been no definite change
in climate in this country during the past hundred years. There
have been variations, such as an excess or a deficiency of rainfall
over a considerable area, that have persisted for several years at
a time; but in each case the conditions would ultimately come back
to normal, or more often to an extreme of the opposite tendency to
what had obtained immediately before. In sections where the rainfall
in bountiful years is barely sufficient for good crops, the people
in the past have been prone to consider that the amount that they
receive during the periods of excess is that which normally is due
them, and thus to be unprepared for the dry periods that statistics
tell us must certainly come. The matter of change of climate is
most important to our sub-arid West,—to the western parts of Texas,
Oklahoma, Kansas, Nebraska, and the Dakotas. Some years ago, when the
tide of emigration was strong into these regions, there were several
years of more than the average rainfall. The coming of population
and the coming of extra rainfall were accidentally coincident, but
that fact was probably responsible for the popular belief that
civilization brings an increase in precipitation; that the breaking
of the virgin soil, making it more permeable to the absorption of
moisture; the planting of trees and the growth of crops, restricting
the run-off; the roots of the new vegetable life drawing up the
moisture from below the surface of the ground and transpiring it
to the air through the leaves of plants; the enormous quantities
of water vapor ejected into the air by the combustion necessarily
incident to a considerable population,—all had combined to increase
the rainfall and render the sub-arid plains more responsive to
the efforts of the husbandman. No one can fail to regret that this
theory is not founded upon fact. But a moment’s thought by the
scientist will indicate to him that the volume of air is so great,
and under the heat of the growing period its capacity for moisture so
enormous, that the addition of vapor of water by the processes herein
described, great though it be, is ineffectual to appreciably change
the amount of the rainfall that nature beforehand had ordained should
be precipitated.
The size of continental areas, the height and the trend of mountain
ranges, the proximity of large bodies of water, and the direction
of the prevailing winds are the factors that determine the amount
of the precipitation of a region. Against these the puny efforts of
man, stupendous though we think them to be, are entirely unavailing.
As an illustration: If the Rocky Mountains were as old as the
Appalachian Chain, and if they were eroded down to the height of the
latter system, the winds from the Pacific Ocean, when they are drawn
inland by the cyclonic storms of the Rocky Mountain plateau, or of
the Mississippi Valley, instead of depositing their moisture on the
west slopes of the first range of mountains, would carry the water
vapor of the Pacific clear to that place in the Mississippi Valley
where it would meet the moisture drawn by the same storms from the
Gulf of Mexico and the Atlantic Ocean. This will appear clear when
one understands that cyclonic storms, such as are continually passing
across our continent in periods of about three days each, may embrace
in their eddy-like circulating systems areas one to three thousand
miles in diameter, in which the winds from all directions spirally
flow towards the center of the cyclonic system and the system itself
is moving eastward.
The water vapor exists as a separate atmosphere from oxygen and
nitrogen. It is screened off from the interior of continents by
mountain ranges because it is condensed and precipitated as rain or
snow at only moderate elevations. The windward side of mountains may,
therefore, receive torrential rains while their leeward sides are
entirely without precipitation.
It follows that if the Rocky Mountains were lowered as described,
the entire United States would be green with rich vegetation and
there would be no deserts anywhere within its broad boundaries. Also,
if the Appalachian Range were as high as the Rocky Mountains—as it
may have been at one time—and if it extended around the Gulf of
Mexico as well as up through our Atlantic Coast States, the vaporous
atmosphere of the Atlantic Ocean and of the Gulf of Mexico would be
prevented from entering the interior of the continent, and the power
that to-day stands as the greatest bulwark of civilization would not
exist. There would be but a narrow fringe of vegetation upon its east
and its west coasts; the interior, with its vast cotton and cereal
plains, would be a barren waste.
But to revert for a moment to Jefferson. He took his thermometer to
Philadelphia when he proceeded there on a mission that would have
caused any less serene and courageous spirit to forget all the small
details of life. When the debates upon which hung the fate of a
nation and, in fact, the lives of those that participated, were in
progress, he coolly hung his thermometer on the wall and noted down
its readings. Those historians who have described the intense heat
in Independence Hall on the Fourth of July, 1776, were mistaken, as
will be shown by reference to his observations, the early and the
late ones of which doubtless were made at his lodgings. They are as
follows: 6 A.M., 68°; 9 A.M., 72¼°; 1 P.M., 76°; and 9 P.M., 73½°.
Jefferson had one of the only two barometers in this country at that
time. James Madison (the Bishop, not the President) had the other.
They took readings at the same hour of the day for a considerable
period of time, and Jefferson discovered that changes in the pressure
of the air always began on his instrument a few hours before they
did on his friend’s instrument a couple of hundred miles to the
east of him. He came near discovering the fact that no matter what
the direction of the wind, storms almost universally move from the
west toward the east. When the British captured Washington they also
raided Monticello, Jefferson’s home in Virginia, and they destroyed
his barometer. It has been said that he was as much distressed over
the loss of his special instrument of science as he was over the
burning of the National Capitol.
In “Descriptive Meteorology” (Appleton), the writer expressed doubt
that there had been important changes in climate within the period
of authentic history, but recent researches cause him to change his
opinion, for the evidence now seems almost conclusive that marked
changes have occurred. The powerful kingdoms of Sumeria, Babylonia,
Assyria, and Persia, each ruling many centuries and dominating all
or a large part of the vast region from the Persian Gulf to the
Caspian Sea and westward to the Mediterranean and Egypt, covering in
their various reigns some four thousand years before Christ, could
hardly have built their many great cities, supported their numerous
millions of population, and developed the trade and commerce that
was theirs with the climatic conditions as they exist to-day. As
late as the opening of the Christian Era, Palmyra, in Syria, had a
population of from one hundred and fifty thousand to two hundred
thousand people, was opulent and adorned with a comparatively high
civilization. To-day we see the wreckage of its vast aqueduct and
irrigating systems, which are unable to gather enough water to wet
their well-constructed walls, and a few hundred people eke out a
miserable existence where once was a metropolis teeming with life
under luxurious conditions. The same picture is shown in more or less
relief throughout the greater part of the region that once maintained
the greatest empires of antiquity. But we must not assume that such
dry and nearly barren conditions are to continue forever; rather are
we to imagine that within a cycle of a few thousand years this region
may have a rebirth of abundant vegetation and again throb with the
pulsations of abounding life.
The record inscribed by the waters on the abandoned and the
submerged shores of inland lakes and seas in the Rocky Mountains,
and on the shores of the Caspian Sea and other waters, is easy to
read. It shows several great oscillations of climate in the United
States and the most civilized portions of the world since the birth
of Christ. For some time before and for several centuries after the
beginning of our era there was a wet period. The Caspian Sea stood
some one hundred feet higher than now and an abandoned beach and a
clearly marked shore line show that Lake Owens, in California, on
the east side of the Sierras, existed at a level nearly two hundred
feet higher than now. There was an abundance of water to irrigate the
Holy Land, and although the center of dominating human power had long
since passed in succession Babylon, Assyria, Persia, Greece, Macedon,
and was working its way towards the Atlantic, the Mesopotamian Valley
was abundantly fruitful.
Then, for six or seven hundred years, with short-period variations
of from thirty to fifty years, the world inhabited by civilized man
and large areas in the temperate zone not yet civilized, grew drier.
The Caspian Sea fell to a lower level than it now maintains, for
the ends of great walls, constructed to keep out barbarians, and
other evidences of the handiwork of man, are now many feet below
the surface of the water. This is the driest time known to history.
Ellsworth Huntington of Yale, acting under the auspices of the
Carnegie Foundation at Washington, made an examination of many of the
stumps of the big trees of California, ranging in age from one to
four thousand years. The thickness of each ring of annual growth is a
legible record of the wetness or the dryness of the year. One would
hardly think of these towering giants of the floral kingdom as being
both thermometers and rain gauges, accurately measuring and recording
the dry-hot and the wet-cold periods for thousands of years, and now
at the end of their majestic careers revealing the hidden secrets
of past ages. Huntington and Cushing, in “Principles of Human
Geography”, say:
“The rings dating from the time of Christ are thick and indicate
that at that time, when Palmyra had an abundant supply of
water, when Owens Lake overflowed and there was high water in
the Caspian Sea, the big trees also had plenty of water and
grew rapidly. Six or seven hundred years later, when Palmyra
was abandoned and when the Caspian Sea stood fifteen or twenty
feet lower than at present, the trees formed only narrow rings,
because the climate was dry. The way in which the growth of
the trees has varied is shown in Figure 30. The high part of
the curve indicates abundant rainfall. The black shading at the
bottom indicates periods of comparative aridity.”
[Illustration: FIG. 30.—Changes in Climate in California during the
Christian Era. Black shading indicates Drought.]
Since the extensive system of observations by the Weather Bureau was
inaugurated, some fifty years ago, it has been revealed to us that
frequently the Ohio Valley would suffer a deficit in rainfall that
would persist for periods as great as five or six years, while New
England and the South Atlantic States, or other large areas of the
country, had an excess. This is an illustration that excesses in
one part of the country were balanced by shortages in other parts
that occurred at the same time. But the long-period oscillations in
climate that are measured in hundreds of years instead of tens—these
changes seemed to have occurred simultaneously in the middle
latitudes of Europe and America. These changes were simultaneous in
an east and west direction. Now we have evidence of such long-period
changes in a north and south direction which were simultaneous, but
of an _opposite character_, indicating that during the Christian Era
the eastward track of storms has oscillated northward and southward.
This would account for the occurrence of dry and of wet periods
simultaneously throughout the vast stretch of territory between
southern California and the Caspian Sea. In Guatemala, Yucatan, and
other Central American countries there are ruins of cities and the
evidence of an agriculture and a civilization that could not have
been established with the torrential rains and jungle growths that
now prevail in those regions. During the centuries when the big
trees of California were receiving a large rainfall and making a
thick annual growth, especially about the beginning of the Christian
Era, because of a northward shifting of the climatic zone, the
precipitation in Yucatan and Guatemala had so diminished as to leave
only the amount of rainfall that could be economically employed in
agriculture and in the rearing of great cities; and then, with a
southward migration of the rain belt, these cities were suffocated
with excessive precipitation, agriculture rendered impossible, and
their temples and palaces buried beneath the gloom of a tropical
growth.
If we are to reason from the records of the past it seems highly
probable that at least the middle latitudes of the Northern
Hemisphere are slowly passing out of a dry period that has prevailed
for the past two hundred years or more. For several hundred years
all the great glaciers have receded, but we should not expect such
recession to continue indefinitely. Geology furnishes abundant
evidence that great changes took place in the climate of the earth
during the prehistoric ages; that there were several glacial periods,
the last occurring during pleistocene times, somewhere between twenty
and fifty thousand years ago, and that there were intervals between
the culminations of the Ice Ages of probably fifty thousand to one
hundred thousand years. Between these long winters, that have meant
death and desolation to much of what are now the most civilized
portions of the earth, there have been warm periods of thousands of
years’ duration.
Fossil remains show that regions far north, now covered with
perpetual ice, once supported a luxuriant flora and fauna, and many
regions in the temperate and equatorial zones that are now deserts
were once overgrown with forests and teeming with animal life. The
fundamental thing of the cosmos is change—birth, growth, maturity;
then decline, senility, death, decay, disintegration; and always
a renaissance, or new birth. Energy and life seem to be eternal,
but ever undergoing change. The Great Ice Cap may again cover New
England, the region of the Great Lakes, and flow southward to the
Ohio River, but the change will be so gradual, if it does come, that
there will be no great cities to be ground beneath the feet of the
boreal monster; cold that will precede the ice cap will destroy them
and they will be buried beneath the dust of accumulating ages before
their icy tombstone is erected. Then the healthful and invigorating
climate of the north part of our country will be transferred to the
region of the Gulf of Mexico. Civilization will and must migrate with
the shifting of the climatic belts. Because these changes cannot
possibly concern us personally, we have almost neglected the study
of the great forces that silently yet most persistently are at work
altering the conditions under which future man must live and work out
the destiny of coming generations.
=Effects of Forests on Climate and Floods.= Next to the fallacious
belief in a change of climate during the life of an individual there
are few if any errors that have gained such wide acceptance as a
belief that the cutting away of the forests has caused a marked
change in climate and especially in the frequency and intensity of
floods and droughts. The writer shared in the mistake with regard to
the influence of the forests in restraining run-off and augmenting
floods, until compelled by an order of the Congress of the United
States to prepare a report on the floods of the nation that had
occurred during the time of the gradual reduction of the forest
areas. Dividing into two equal periods the forty years for which
the Weather Bureau has comprehensive records of the rainfall upon
the catchment basins of the Tennessee, the Cumberland, and the Ohio
rivers, and for which it has records of the height of the rivers,
contrary to his belief, he found that the high waters were no higher
with a given rainfall, the floods of no longer duration, nor the
low waters of summer lower, during the last half of the period than
during the first half.
It is now pretty generally conceded by hydraulic engineers that the
broken, permeable soil of the husbandman, frequently stirred by
cultivation a part of the year and filled with countless billions
of the tiny water-absorbing rootlets of the grasses and the cereal
crops during the remainder of the annual period, is equally as good
a conserver of the rainfall as the forests themselves, even if it is
not better.
Some years ago the writer was delivering a series of Chautauqua
lectures. He arrived at Devil’s Lake, North Dakota, and found that
the Chautauqua amphitheater was on the banks of Devil’s Lake, once
bordering the town, but now receded to a distance of five miles and
confined to a narrow valley. In driving from the city to the lecture
hall he remarked to his escort that they seemed to be traveling along
the bottom of an ancient lake. His companion said, “Yes, a lake, but
not an ancient one. Fifty years ago I used to dive off a springboard
right there in front of the railroad station.” In the course of his
lecture the writer referred to this incident and told them that,
contrary to their belief, their climate had not changed, that fifty
years ago they sold their old lake to some gentlemen in Chicago and
that they had been selling it over again every year since; that the
former compact surface of the virgin prairie resisted the penetration
of the rainfall, or at least only slowly absorbed it, and allowed it
to collect in the depression adjacent to the city; but now, in the
broken, permeable soil of the farmer it was taken up by millions of
tiny rootlets and the hand of the Great Alchemist had transformed
their lake into wheat, the sale of which was responsible for the
presence of the speaker on the platform of a largely-attended
Chautauqua. The lake had gone never to return unless the region were
again to become the haunt of the buffalo and the prairie dog instead
of civilized man. The rainfall was the same, but it was now being
utilized for the benefit of mankind.
In this problem of rainfall, floods, and the forests, most persons
assume that when the forest is cut the land is at once denuded of
vegetation. On the other hand a second growth will effectually shade
the soil within a few months or a few weeks after the large trees
are removed, and if the land is cleared and rendered fit for the
plow, growing crops take the place of the forest-covering the greater
portion of the time.
There is an abundance of reasons for the protection of our
diminishing forests and for the creation of new forest areas without
assigning to the forests functions that they do not exercise. The
covering of an area by a great city, a village, a forest, a barn, or
a tent modifies the climate of the particular area covered so long as
the covering remains, but there is no appreciable climatic effect a
few feet above the surface of the earth between a forest and a field
of grain. The climate of a region like the American continent is
controlled fundamentally by the great oceans that wash its shores,
by the trend of its mountain systems and their height, and by the
direction of its prevailing winds. The vast vaporous atmosphere
that flows inland from the Atlantic Ocean to the foothills of the
Rocky Mountains, deluging our cereal plains with its life-giving
precipitation will continue its pluvial generosity without any heed
whatever to the puny scratchings of man upon the surface of Mother
Earth. Nothing that man can do will intensify drought conditions
on this continent or augment the volume of floods. It is time that
we return to sanity in considering this matter instead of being
frightened by the dire forebodings of well-meaning but purely
visionary enthusiasts, no matter how noble their aspirations may be
or how self-sacrificingly they have consecrated themselves to the
redemption of humanity.
It is certain that forests restrict the flow of moderate falls of
rain, but they do not restrain the flow of flood waters, because,
surprising as it may seem to one who has not tested the matter,
floods do not occur until after all surfaces, open fields and forests
alike, have become saturated, and then the run-off of the two
surfaces is equal.